Forced circulation boiler with internal circulating tubes



Aug. 4, 1964 E. WAHL ETAL FORCED CIRCULATION BOILER WITH INTERNAL CIRCULATING TUBES 3 Sheets-Sheet 1 Filed June 5, 1959 INVEN TOPs u w a M N L D My 0 2 I I w 7 a? w I I M 1L 8.

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Aug. 4, 1964 E. WAHL ETAL FORCED CIRCULATION BOILER WITH INTERNAL CIRCULATING TUBES 3 Sheets-Sheet 3 Filed June 5, 1959 I] if axqa a aal gaqsidd '1 (NVENTOPS LJ WMM United States Patent The present invention relates to boilers in general, and more particularly to a forced circulation boiler with internal circulating tubes which form a wall or lining for the furnace chamber and for at least a portion of the uptake.

An important object of the invention is to provide a horizontal or vertical boiler which is so constructed that the products of combustion are positively prevented from escaping through and from attacking the metallic parts of the walls.

Another object of the invention is to provide a forced circulation boiler in which the products of combustion are restricted to a single path vertically upwardly through the furnace chamber and the uptake.

A further object of the invention is to provide a boiler of the type known as a single-pass forced circulation boiler which is so constructed that the combustion in its furnace chamber may be readiy inspected at one or more points; which needs no external lagging on its outer casing; and in which the tubing for forced circulation of a fluid medium may be so arranged that no intermediate headers are required.

The above and many other objects of the invention are attained by the provision of a boiler which comprises two spaced metallic shells which form therebetwen a space, and means for introducing into the space a fluid medium at pressures higher than those prevailing in the furnace chamber and in the uptake. In such manner, the gaseous products of combustion are positively prevented from escaping through the walls of the boiler and are restricted to passage in upward direction through the uptake and into the chimney to heat certain piping located in their path and containing a fluid medium which should be heated to a given extent. As is known, the fire gases in oilor gas-fired boilers contain aggressive sulphur-oxygen compounds which form highly corrosive deposits when they cool, and which therefore cause considerable destructive damage to the colder structural metal parts of the boiler. The above described space between the shells of the boiler positively prevents contact of such highly corrosive compounds with the metallic casing of the boiler. Moreover, the heat-protecting lagging is located inside the supporting external shell so that the latter may be devoid of any kind of heat protection and hence easy to inspect from the outside.

The inner shell surrounds the steaming tubes which form the walls of the furnace chamber and of the uptake, and comprises expansion elements in the form of corrugations to compensate for and to follow the heat expansion of other component parts of the boiler. The outer shell may consist of a unitary structure or of separate sections with flanged rings joined end-to-end and preferably reinforced by profiled rods. The inner and the outer shell may be of circular or polygonal cross-sectional contour.

Suitable entry doors which can be closed in gas-tight fashion are provided for the inspection of the inside of the outer supporting sheet metal shell and of the interior of the uptake. Also, observation tubes are provided to facilitate inspection of the interior of the furnace chamber. All pipe connections which pass through the external shell are taken through glands or the like adapted to move in every direction for sealing the external shell 3,143,1fl2 Fatented Aug. 4., 1964 and for permitting it to contain the raised pressure inside.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following descripion of certain specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a vertical section through a field boiler embodying the invention;

FIG. 2 is a vertical section through the field boiler taken at right angles to the section of FIG. 1;

FIG. 3 is a horizontal section taken on line IIIIII of FIG. 2, as seen in the direction of arrows;

FIG. 4 is a horizontal section taken on line IVIV of FIG. 1, as seen in the direction of arrows;

FIG. 5 illustrates in vertical section a modified arrangement of tubing in the uptake of the boiler;

FIG. 6 is a horizontal section taken on the line VIVI of FIG. 5, as seen in the direction of arrows;

FIG. 7 is a horizontal section taken on the line VII-- VII of FIG. 5, as seen in the direction of arrows; and

FIG. 8 illustrates on a larger scale the manner in which certain tubes shown in FIG. 5 are supported on and connected with each other.

Referring now in greater detail to the drawings, and first to FIG. 1 the boiler B stands on a supporting ring 10 resting on a concrete or like foundation 11. Built into the floor of the boiler furnace F is a burner 12 which is supplied with the necessary combustion air through a duct 13. The tube lining 15 of the furnace chamber 16 stands on the bottom layer 14 of the floor structure of the furnace F. The tube lining 15 may consist of a helical coil comprising several parallel tubes as is shown in FIGS. 1 and 2, or of parallel meandering groups of tubes which run to and fro up the inner sides of the furnace F. Toward the top of the furnace chamber 16, the cross-section of the latter is somewhat narrowed, as at 17, the tube lining 15 extending in upward direction beyond this constriction. It is preferred to impart to the furnace F a polygonal, e.g. square, shape above the constriction 17.

Tube lining 15 is surrounded by a layer 18 of refrac tory material, e.g. fire brick, which in turn is surrounded by a gas-tight sealing sheet metal shell 19 which completely surrounds the furnace chamber 16 and the uptake 21. The outer face of the sheet metal shell 19 is lagged with a heat resistant material 20, such as asbestos, slag or glass wool, of appropriate thickness, which may be supported by a wire mesh or the like. Observation tubes 22 are provided at the point 17 where the cross-section of the furnace F narrows. These observation tubes are welded to the thin sheet metal shell 19 and permit observation of flame formation in the furnace chamber 16. In the illustrated example the Walls of the uptake 21 consist of vertical flat walls of tubing 23 which connect up with headers 24, 25 and 26. Above the point 17 where the cross-section of the furnace chamber 16 narrows, the thin sheet metal shell 11 is provided with an appropriate number of corrugated expansion elements 27 to permit the shell to adapt itself to the thermal expansion of the walls surrounding the furnace chamber 16 and the uptake 21. The latter contains the economizers or contact heat transfer elements 29 to 31. The upper headers 32 with which the economizer 31 is connected are movably suspended from the cross beam 33. An external shell 35 includes an upper reducer part 34 integral with the remainder of the outer shell, and the outer shell including the reducer part surrounds the inner shell 19 and forms with the latter an enclosed space. The upper end of the reducer part 34 is located adjacent the upper end of the uptake 21 and supports the cross beam 33. The cross beam 33 also supports the upper headers 24 of the tubes 23 which form the lateral walls of the uptake 21. Resting on cross beam 33 is a tubular air heater 36, the furnace gases passing straightthrough the same; It is preferred to provide the airheater 36 with an external lagging 37 which may be formed with an external sheet metal skin or the like (not shown). Above the airheater 36 are dampers 38, and the whole is surmounted by the chimney 51. If the boiler B is erected outside, i.e. if it is a so-called field boiler, it is desirable to construct it in the proximity of a building 3% which houses and shelters various control devices, the superheated steam cooler 53, the air blower and certain other apparatus. All tubing leading from the boiler B to building 39 passes through suitable glands (not shown) and is articulately connected with the headers so as to be movable in all directions, the glands sealing the outer shell and permitting it to contain raised pressure in the space S therewithin.

Referring now to FIG. 2, there is shown a blower which constitutes means for forcing fresh air into the draught box 41. At the same time fresh air at the static pressure of blower 40 is forced through a branch line 42 into the space S inside the supporting sheet metal shell 35. Thus, the pressure in the space S between shells 19 and 35 is always somewhat higher than that in the furnace chamber 16 or in the uptake 21. Slight pressure losses inside the shell 35 are compensated for by the blower 40 through its branch line or conduit 42 so that the static pressure in the space S inside the sheet metal shell 35 will be maintained. The combustion air which is preheated while passing from draught box 41 about the elements of heater 36 reaches the duct 13 and thence the burner 12 through a thermally insulated duct 43 comprising heat expansion elements 43a. The airheater 36 communicates with the duct 43. The external shell 35 is fitted with several entry doors 44 which close in a gas-tight manner and which are located opposite, i.e. aligned with, entry doors .5 in the walls surrounding the gas uptake 21. Shell 35 and eventually the shell 19 may consist of several sections formed with flanged rings which may be reinforced by profiled rods or the like.

For the purpose of facilitating observation of the burner month, an additional observation tube 46 is provided at an appropriate height. Thus tube, in the same way as the previously mentioned observation tubes 22, projects from a stub pipe 47 which is welded to the external shell 35 and has sufficient freedom to adapt itself to thermal movements of the wall of the furnace chamber 16. FIG. 2 further shows that the contact tube bundles 29 to 31 and the superheater 28 are suspended from cooled faller tubes 48 carried by the upper headers 32.

The products of combustion developing in burner 12 ascend in the chamber 16 and uptake 21 to heat the tubes 15, 2831 and those of airheater 36, and to be thereupon discharged through dampers 38 and chimney 51.

FIG. 3 shows in cross-section the upper end of the uptake 21 and the lower ends of vertical air tubes forming part of the airheater 36. Four box-section columns 49 are arranged at the corners of device 36 and support the transition member 50 (see FIG. 2) which contains the aforementioned dampers 38 and carries the superimposed chimney 51.

FIG. 4 illustrates the superheater 28 in uptake 21; the entry tubes to this superheater extend from a header 52 which communicates with the superheated steam cooler 53 located in the housing 39 (see FIG. 1). It will be seen that the uptake 21 is of substantially square crosssectional contour.

Since the pressure in space S exceeds the pressure in chamber 16 and uptake 21, the passage of corrosive sulphur-oxygen compounds through the layers 18-20 into the space S is positively prevented. Such compounds constitute byproducts developing during the combustion of fuel in burner 12. V

FIGS. 5 to 8 illustrate the details of a modified layout of tubing in a circular uptake 21'. In the form of construction shown in FIG. 5, the tubing surrounding the uptake 21' is formed by two parallel tubes 54, 55 which are helically coiled to define a cylindrical casing. At the top of the first or lower part of the uptake 21', the lower tube 55 is bent inwardly to form an upper horizontal coil 56. The tubes 54, 55 which are now conducted in the form of meandering coils 57 and rise in upward direction from the horizontal plane, as shown in FIG. 6, rest on the horizontal coil 56. Above each meandering coil 57, a further ring-shaped coil 58 consisting of tubes 54, 55 arranged one inside the other is formed and so forth, until the required heating surface has been made up and the tubes are again led in the form of a cylindrical helix 59. Entry openings 60 may be provided in the cylindrical sections of tubes 54, 55 above and below their zones 56-58.

The economizer in the upper part of the uptake 21' utilizes a different layout of tubing with narrower gaps therebetween, as is shown in FIGS. 5 and 7. Each of the two tubes 61, 62 is bent over in cruciform fashion, as is shown at 63 in FIG. 7, whereupon the tubes drop downwardly near the axis of the boiler to return to the outer periphery in the form of a spiral 64, to then descend obliquely a distance equaling two tube diameters and to be again bent inwardly in cruciform fashion, spirally returned to the outside, and so forth, until the required heating surface has been made up. The ends 65, 66 of tubes 61, 62, respectively, may either be taken to the outside or so arranged as to connect directly with the cylindrical wall-forming helix 59.

FIG. 8 illustrates, drawn to a larger scale, the manner in which the several coils of the tubing rest the one on the other, and how support is provided at the point where the horizontal ledge is formed at 56 (see FIG. 5). The individual coils of tubes 54, 55 are separated by spacers 67 and, when the cylindrical portion has thus been erected, an adapter 68 is welded into position from the outside for adjusting the helix to accurate vertical alignment. A special intermediate member 69 at the upper end of the helix establishes the spacing between the tubes, and a supporting ledge 70 on the latter holds the inner coils at a point 71 (see FIG. 5).

The entire boiler, i.e. the furnace chamber 16 and the gas uptake 21' may thus be lined with tubes without the necessity of providing intermediate headers. The feed water enters at 61, 62 in the direction of arrows shown at the top of FIG. 5, to be conducted via tubing 65, 66 to pipes 54, 5S and to leave the upper end of the tube helix 59 in the form of a saturated or slightly superheated steam.

Instead of being of vertical type, the boiler could be constructed as a horizontal boiler provided the support means inside the boiler were appropriately modified.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for vari ous modifications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptions should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A forced circulation boiler comprising, in combination: an inner shell defining therewithin a furnace chamber and an uptake communicating with the chamber;

tubing lining the furnace chamber and the uptake; an air-heater on the top of the uptake; an external gas tight shell supporting the airheater and the tubing in the uptake, said external shell surrounding the inner shell and forming with the latter an enclosed space; and means for producing and maintaining in said space a static gas pressure higher than the pressures prevailing in the chamber and in the uptake whereby the products of combustion developing in the chamber are prevented from penetrating through the inner shell.

2. A forced circulation boiler comprising, in combination: an inner shell defining therewithin a furnace chamber and an uptake communicating with the chamber; tubing lining the furnace chamber and the uptake; at tubular airheater located above the uptake; an external gas tight shell supporting the airheater and the tubing in the uptake, said external shell surrounding the inner shell and forming with the latter an enclosed space; and means for circulating combustion air about said airheater, for conveying heated air externally of said external shell from the airheater to the chamber, and for forcing air into the space to provide therein a static gas pressure higher than the pressures prevailing in the chamber and in the uptake whereby the products of combustion developing in the chamber are prevented from penetrating through the inner shell.

3. A forced circulation boiler comprising, in combination: an inner shell defining therewithin a furnace chamber and an uptake communicating with the furnace chamber, said inner shell having at least one corrugated heat expansion element adjacent the upper end of said chamber for permitting expansion and contraction of said inner shell at varying temperatures; an external gas tight carrying shell surrounding the inner shell and forming with the latter an enclosed space, the external shell having an upper (end adjacent to the upper end of the uptake; a cross beam supported by the upper end of the external shell; first tubing lining the furnace chamber in the inner shell; second tubing suspended from the cross beam and lining the uptake; an airheater located above and sup ported on the cross beam; and means for producing and maintaining in the space a static gas pressure higher than the pressures prevailing in the furnace chamber and in the uptake whereby the products of combustion developing in the furnace chamber are prevented from penetrating through the inner shell and are discharged through the uptake, through the airheater and through the chimney.

References Cited in the file of this patent UNITED STATES PATENTS 754,837 Barton Mar. 15, 1904 1,779,276 Jacobus Oct. 21, 1930 1,819,174 Jacobus Aug. 18, 1931 1,922,663 Kernnal Aug. 15, 1933 1,975,096 Fletcher Oct. 2, 1934 2,012,216 Baumann- Aug. 20, 1935 2,179,638 Koppers Nov. 14, 1939 2,251,014 Firshing July 29, 1941 2,268,559 Bailey Jan. 6, 1942 2,291,872 Brantly Aug. 4, 1942 2,736,400 Gay et al. Feb. 28, 1956 2,864,344 Artsay Dec. 16, 1958 FOREIGN PATENTS 455,118 Germany Feb. 9, 1927 762,416 Germany May 15, 1951 

1. A FORCED CIRCULATION BOILER COMPRISING, IN COMBINATION: AN INNER SHELL DEFINING THEREWITHIN A FURNACE CHAMBER AND AN UPTAKE COMMUNICATING WITH THE CHAMBER; TUBING LINING THE FURNACE CHAMBER AND THE UPTAKE; AN AIR-HEATER ON THE TOP OF THE UPTAKE; AN EXTERNAL GAS TIGHT SHELL SUPPORTING THE AIRHEATER AND THE TUBING IN THE UPTAKE, SAID EXTERNAL SHELL SURROUNDING THE INNER SHELL AND FORMING WITH THE LATTER AN ENCLOSED SPACE; AND MEANS FOR PRODUCING AND MAINTAINING IN SAID SPACE A STATIC GAS PRESSURE HIGHER THAN THE PRESSURES PREVAILING IN THE CHAMBER AND IN THE UPTAKE WHEREBY THE PRODUCTS OF COMBUSTION DEVELOPING IN THE CHAMBER ARE PREVENTED FROM PENETRATING THROUGH THE INNER SHELL. 